CN113972366B - A kind of positive electrode sheet of secondary battery and secondary battery - Google Patents

Abstract

In order to overcome the problem of insufficient safety performance of existing secondary batteries, the present invention provides a secondary battery positive electrode sheet, which includes a positive electrode material layer. The positive electrode material layer includes a positive electrode active material and a compound represented by structural formula 1: The positive electrode active material includes M element, and the M element is selected from one or two types of Mn and Al. The positive electrode material layer satisfies the following conditions: 0.05≤p·u/v≤15, where u is the positive electrode material layer. The mass percentage content of phosphorus element, unit is wt%; v is the mass percentage content of M element in the cathode material layer, unit is wt%; p is the single surface density of the cathode material layer, unit is mg/cm ² . At the same time, the invention also discloses a secondary battery including the above-mentioned positive electrode sheet. The present invention rationally quantifies the factors of the compound shown in Structural Formula 1, Mn and Al elements, and single surface density, and obtains a secondary battery with high energy density and excellent safety performance.

Description

A secondary battery positive electrode sheet and secondary battery

Technical Field

The invention belongs to the technical field of energy storage electronic components, and in particular relates to a secondary battery positive electrode sheet and a secondary battery.

Background Art

Since lithium-ion batteries were put on the market in 1991, they have been widely used in mobile communications, laptops and other fields because of their advantages such as high operating voltage, long cycle life, high energy density and no memory effect. The charging and discharging process of lithium-ion batteries is the process of lithium ions being embedded and de-embedded in the positive and negative electrodes. The positive electrode sheet made of positive electrode materials is the only (or main) provider of lithium ions in lithium-ion batteries. The type of positive electrode material also determines the energy density of lithium-ion batteries.

As lithium-ion secondary batteries are increasingly used, people have put forward higher requirements for the safety performance of lithium-ion secondary batteries. Lithium-ion secondary batteries using ternary system positive electrode active materials have large discharge capacity and high energy density, and are very potential lithium-ion secondary batteries, but the safety performance of this type of lithium-ion secondary battery is poor. As people put forward higher and higher requirements for the performance of lithium-ion secondary batteries, in addition to having excellent high-temperature storage and cycle performance, how to make lithium-ion secondary batteries have high safety performance has become a technical problem that needs to be overcome. In particular, as a power source for electric vehicles or electronic products, the safety of lithium-ion secondary batteries under different conditions is directly related to the life safety of the operator.

Summary of the invention

In view of the problem that existing lithium-ion secondary batteries have insufficient safety performance, the present invention provides a secondary battery positive electrode sheet and a secondary battery.

The technical solution adopted by the present invention to solve the above technical problems is as follows:

In one aspect, the present invention provides a secondary battery positive electrode sheet, comprising a positive electrode material layer, wherein the positive electrode material layer comprises a positive electrode active material and a compound shown in structural formula 1:

wherein R ₁ , R ₂ , and R ₃ are each independently selected from an alkyl group of 1 to 5 carbon atoms, a fluoroalkyl group of 1 to 5 carbon atoms, an ether group of 1 to 5 carbon atoms, a fluoroether group of 1 to 5 carbon atoms, and an unsaturated hydrocarbon group of 2 to 5 carbon atoms, and at least one of R ₁ , R ₂ , and R ₃ is an unsaturated hydrocarbon group of 2 to 5 carbon atoms;

The positive electrode active material includes an M element, and the M element is selected from one or both of Mn and Al;

The positive electrode material layer meets the following conditions:

0.05≤p·u/v≤15

Wherein, u is the mass percentage of phosphorus in the positive electrode material layer, in wt%;

v is the mass percentage of the M element in the positive electrode material layer, in wt%;

p is the single-surface density of the positive electrode material layer, and its unit is mg/cm ² .

Optionally, the positive electrode material layer meets the following conditions:

0.1≤p·u/v≤10;

Preferably, the positive electrode material layer meets the following conditions:

0.5≤p·u/v≤5.

Optionally, the compound shown in structural formula 1 includes at least one of tripropargyl phosphate, dipropargyl methyl phosphate, dipropargyl fluoromethyl phosphate, dipropargyl methoxymethyl phosphate, dipropargyl ethyl phosphate, dipropargyl propyl phosphate, trifluoromethyl dipropargyl phosphate, dipropargyl 2,2,2-trifluoroethyl phosphate, dipropargyl 3,3,3-trifluoropropyl phosphate, hexafluoroisopropyl dipropargyl phosphate, triallyl phosphate, diallyl methyl phosphate, diallyl ethyl phosphate, diallyl propyl phosphate, trifluoromethyl diallyl phosphate, 2,2,2-trifluoroethyl diallyl phosphate, dipropargyl methyl ether phosphate, dipropargyl fluoromethyl ether phosphate, diallyl 3,3,3-trifluoropropyl phosphate or diallyl hexafluoroisopropyl phosphate.

Optionally, the surface of the positive electrode material layer is detected by X-ray photoelectron spectroscopy, and when the 1s peak of carbon is obtained at 284.5 eV, a characteristic peak of phosphorus element appears in the region of 130 to 140 eV.

Optionally, in the positive electrode material layer, the mass percentage content u of phosphorus element is 0.1wt% to 3wt%;

Preferably, in the positive electrode material layer, the mass percentage content u of phosphorus element is 0.1wt% to 2wt%.

Optionally, in the positive electrode material layer, the mass percentage content v of the M element is 3wt% to 60wt%;

Preferably, in the positive electrode material layer, the mass percentage v of the M element is 3wt% to 30wt%.

Optionally, the single-surface density p of the positive electrode material layer is 10 to 30 mg/cm ² ;

Preferably, the single surface density p of the positive electrode material layer is 15-20 mg/cm ² .

Optionally, the compound represented by structural formula 1 is formed on the surface of the positive electrode material layer, or the compound represented by structural formula 1 is mixed in the interior of the positive electrode material layer.

On the other hand, the present invention provides a secondary battery, comprising a negative electrode, a non-aqueous electrolyte and the secondary battery positive electrode as described above, wherein the non-aqueous electrolyte comprises a non-aqueous organic solvent, and the non-aqueous organic solvent comprises a cyclic carbonate.

Optionally, the non-aqueous electrolyte also includes a lithium salt, and the lithium salt includes _{one or more} of _LiPF6 , _LiBOB , LiDFOB, LiPO2F2, _LiBF4 , LiSbF6, _LiAsF6 , LiN( _SO2CF3 ) ₂ , LiN( _SO2C2F5 ) ₂ , LiC( _SO2CF3 ) _{, LiN (} SO2F) _{2 , LiClO4 , LiAlCl4} , _LiCF3SO3 , _Li2B10Cl10 , _and lower aliphatic carboxylic _{acid lithium} salts.

According to the positive electrode provided by the present invention, the compound shown in structural formula 1 is added to the positive electrode material layer, and the relationship between the mass percentage content u of phosphorus element, the mass percentage content v of Mn and/or Al element and the single-surface surface density p of the positive electrode material layer is reasonably designed. When the positive electrode material layer satisfies the condition 0.05≤p·u/v≤15, the synergistic effect between the compound shown in structural formula 1 and the element selection and single-surface surface density of the positive electrode active material can be fully exerted, so that the positive electrode active material has a higher structural stability, the side reaction of the non-aqueous electrolyte on the surface of the positive electrode material layer is significantly reduced, and in particular, the thermal shock resistance of the battery is also significantly improved, and the battery safety performance is greatly improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an XPS spectrum of the positive electrode sheet in the secondary battery provided in Example 3 of the present invention.

DETAILED DESCRIPTION

In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

An embodiment of the present invention provides a secondary battery positive electrode sheet, comprising a positive electrode material layer, wherein the positive electrode material layer comprises a positive electrode active material and a compound shown in structural formula 1:

wherein R ₁ , R ₂ , and R ₃ are each independently selected from an alkyl group of 1 to 5 carbon atoms, a fluoroalkyl group of 1 to 5 carbon atoms, an ether group of 1 to 5 carbon atoms, a fluoroether group of 1 to 5 carbon atoms, and an unsaturated hydrocarbon group of 2 to 5 carbon atoms, and at least one of R ₁ , R ₂ , and R ₃ is an unsaturated hydrocarbon group of 2 to 5 carbon atoms;

The positive electrode active material includes an M element, and the M element is selected from one or more of Mn and Al. The positive electrode material layer meets the following conditions:

0.05≤p·u/v≤15

Wherein, u is the mass percentage of phosphorus in the positive electrode material layer, in wt%;

v is the mass percentage of the M element in the positive electrode material layer, in wt%;

p is the single-surface density of the positive electrode material layer, and its unit is mg/cm ² .

In the present invention, the compound shown in structural formula 1 is added to the positive electrode material layer. Since the compound shown in structural formula 1 is an unsaturated phosphate ester with a specific structure, it covers the surface of the positive electrode active material, which greatly improves the flame retardant performance of the positive electrode material layer. At the same time, the inventors found that the compound shown in structural formula 1 has a large difference in the coordination effect with different positive electrode active materials and positive electrode material layers with different single-sided surface densities. In particular, the compound shown in structural formula 1 has a good affinity with Mn and Al elements, and the coordination of the two has a certain improvement effect on the stability of the positive electrode active material in long-term cycles. In addition, the compound shown in structural formula 1 will inevitably occupy the alkali metal ion insertion and extraction sites of the positive electrode active material. This is particularly evident when the single-surface surface density of the positive electrode material layer is too high or too low. It is speculated that after the compound shown in structural formula 1 is added, its interaction with the Mn and Al elements and the single-surface surface density affects the migration of alkali metal ions in the positive electrode material layer, and has a direct impact on the internal resistance and high-rate charge and discharge performance of the battery. At the same time, the compound shown in structural formula 1, the selection of the positive electrode active material and the single-surface surface density of the positive electrode material layer also affect the stability of the passivation film on the surface of the positive electrode material layer. Therefore, the inventors comprehensively considered the design of experiments and summarized the relationship of 0.05≤p·u/v, and rationally quantified the factors of the compound shown in structural formula 1, the Mn and Al elements and the single-surface surface density, thereby obtaining a battery with high energy density and excellent safety performance.

In a preferred embodiment, the positive electrode material layer satisfies the following conditions:

0.1≤p·u/v≤10.

In a more preferred embodiment, the positive electrode material layer satisfies the following conditions:

0.5≤p·u/v≤5.

When the mass percentage u of phosphorus element, the mass percentage v of Mn and/or Al element in the positive electrode material layer and the single surface density p of the positive electrode material layer are within the above relationship range, the thermal shock resistance of the battery can be further improved.

It should be noted that in the above relationship, the phosphorus element in the positive electrode material layer only represents the phosphorus element derived from the compound shown in Structural Formula 1, and the M element in the positive electrode material layer only represents the Mn and/or Al element derived from the positive electrode active material.

In the present invention, when the positive electrode active material contains only Mn element, the mass percentage of M element in the positive electrode material layer refers to the mass percentage of Mn element; when the positive electrode active material contains only Al element, the mass percentage of M element in the positive electrode material layer refers to the mass percentage of Al element; when the positive electrode active material contains both Al and Mn elements, the mass percentage of M element in the positive electrode material layer refers to the sum of the mass percentages of Al element and Mn element.

In the description of the present invention, the term "single-sided surface density of the positive electrode material layer" refers to the coating weight of the positive electrode material layer on a single side of the positive electrode per unit area. The coating weight test method can be adopted as follows: take 30 pieces of current collector foil, each of which has an area of S1, weigh them respectively, and take the average value, which is recorded as W1; coat the same weight of slurry on a single side of each piece of current collector foil, and after coating evenly, dry it at 120°C for 1 hour. After testing to find that it is basically free of solvent, weigh the current collector foil coated with slurry on a single side after drying, and take the average value, which is recorded as W2; then the surface density of the single-sided active material layer on the current collector can be obtained as W=(W2-W1)/S1.

In the present invention, the alkyl group of 1-5 carbon atoms can be selected from, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, sec-pentyl or neopentyl; the fluoroalkyl group of 1-5 carbon atoms is selected from the group obtained by replacing one or more hydrogen elements in the alkyl group of 1-5 carbon atoms with fluorine elements.

The unsaturated hydrocarbon group of 2 to 5 carbon atoms may be selected from, for example, vinyl, propenyl, allyl, butenyl, pentenyl, methylvinyl, methylallyl, ethynyl, propynyl, propargyl, butynyl, pentynyl.

The ether group of 1 to 5 carbon atoms may be selected, for example, from methyl ether, ethyl ether, methyl ethyl ether, propyl ether, methyl propyl ether, ethyl propyl ether.

The fluorinated ether group of 1 to 5 carbon atoms may be selected from, for example, fluoromethyl ether, fluoroethyl ether, fluoromethylethyl ether, fluoropropyl ether, fluoromethylpropyl ether, fluoroethylpropyl ether.

In some embodiments, the compound shown in structural formula 1 includes at least one of tripropargyl phosphate, dipropargyl methyl phosphate, dipropargyl fluoromethyl phosphate, dipropargyl methoxymethyl phosphate, dipropargyl ethyl phosphate, dipropargyl propyl phosphate, trifluoromethyl dipropargyl phosphate, dipropargyl 2,2,2-trifluoroethyl phosphate, dipropargyl 3,3,3-trifluoropropyl phosphate, hexafluoroisopropyl dipropargyl phosphate, triallyl phosphate, diallyl methyl phosphate, diallyl ethyl phosphate, diallyl propyl phosphate, trifluoromethyl diallyl phosphate, 2,2,2-trifluoroethyl diallyl phosphate, dipropargyl methyl ether phosphate, dipropargyl fluoromethyl ether phosphate, diallyl 3,3,3-trifluoropropyl phosphate or diallyl hexafluoroisopropyl phosphate.

The above compounds may be used alone or in combination of two or more.

In some embodiments, the surface of the positive electrode material layer is detected by X-ray photoelectron spectroscopy. When the 1s peak of carbon is obtained at 284.5 eV, a characteristic peak of phosphorus element appears in the region of 130 to 140 eV, as shown in FIG. 1 , indicating that the compound shown in structural formula 1 participates in the formation of a passivation film on the surface of the positive electrode material layer.

In some embodiments, in the positive electrode material layer, the mass percentage content u of phosphorus element is 0.1wt% to 3wt%.

In a preferred embodiment, in the positive electrode material layer, the mass percentage content u of phosphorus element is 0.1wt% to 2wt%.

Specifically, in the positive electrode material layer, the mass percentage u of phosphorus element can be 0.1wt%, 0.2wt%, 0.5wt%, 0.8wt%, 1.0wt%, 1.5wt%, 2.0wt%, 2.5wt% or 3wt%.

The phosphorus element is derived from the compound shown in Structural Formula 1, and its mass percentage is positively correlated with the added amount of the compound shown in Structural Formula 1. Since the compound shown in Structural Formula 1 contains phosphorus-containing groups, it has good flame retardant properties; and it can form a stable phosphorus-containing passivation film on the interface where the positive electrode material layer contacts the non-aqueous electrolyte. The passivation film can inhibit excessive side reactions between the positive electrode material layer and the non-aqueous electrolyte, effectively preventing manganese or aluminum ions dissolved in the positive electrode active material from entering the negative electrode active material, thereby improving the structural stability of the positive and negative electrode active materials, and thus improving the thermal stability of the lithium ion battery.

In some embodiments, in the positive electrode material layer, the mass percentage content u of phosphorus element is 0.1wt% to 3wt%;

In a preferred embodiment, in the positive electrode material layer, the mass percentage v of the M element is 3wt% to 60wt%.

Specifically, the mass percentage v of the M element can be 3wt%, 5wt%, 8wt%, 10wt%, 12wt%, 15wt%, 21wt%, 23wt%, 27wt%, 30wt%, 36wt%, 42wt%, 48wt%, 50wt%, 55wt% or 60wt%.

The manganese element or aluminum element in the positive electrode active material can ensure the structural stability of the positive electrode active material, reduce the decomposition and deoxygenation of the positive electrode active material, inhibit gas production, reduce heat production, thereby reducing the risk of runaway of the secondary battery, and making the secondary battery have higher safety performance.

In some embodiments, the single-surface density p of the positive electrode material layer is 10 to 30 mg/cm ² ;

In a preferred embodiment, the single-surface density p of the positive electrode material layer is 15-20 mg/cm ² .

Specifically, the single-surface density p of the positive electrode material layer may be 10 mg/cm ² , 12 mg/cm ² , 14 mg/cm ² , 16 mg/cm ² , 18 mg/cm ² , 21 mg/cm ² , 24 mg/cm ² , 28 mg/cm ² or 30 mg/cm ² .

The single-sided surface density of the positive electrode material layer is a key technical parameter in the design and production of secondary batteries. Under the same length of the positive electrode plate, if the single-sided surface density of the positive electrode material layer is large, the capacity of the battery will increase, and the temperature rise of the battery during charging will increase, affecting the safety performance; while if the single-sided surface density of the positive electrode plate is small, the capacity of the battery will decrease, and the temperature rise of the battery during charging will be small.

The above analysis is only based on the impact of each parameter on the battery when it exists alone, but in the actual battery application process, the above three parameters are interrelated and inseparable. The relationship given by the present invention relates the three, and the three jointly affect the capacity and thermal shock resistance of the battery. Therefore, the ratio of the mass percentage of phosphorus element and M element in the positive electrode sheet and the single-sided surface density of the positive electrode material layer design parameters are adjusted to make 0.05≤p·u/v≤15, which can effectively improve the safety performance and other properties of lithium-ion secondary batteries while ensuring that the secondary battery has a higher specific capacity and energy density. If the p·u/v value is too high or too low, the battery will experience kinetic deterioration, which makes the battery prone to fire in extreme environments, posing a safety hazard.

In some embodiments, the positive electrode active material includes one or more of the compounds represented by formula (1) and formula (2);

Li _1+x Ni _a Co _b M _1-ab O _2-y A _yFormula (1)

Li _1+z Mn _c L _2-c O _4-d B _dFormula (2)

In formula (1), -0.1≤x≤0.2, 0<a<1, 0≤b<1, 0<a+b<1, 0≤y<0.2, M includes one or more of Mn and Al, and optionally includes zero, one or more of Sr, Mg, Ti, Ca, Zr, Zn, Si, Fe, Ce, and A includes one or more of S, N, F, Cl, Br and I;

In formula (2), -0.1≤z≤0.2, 0<c≤2, 0≤d<1, L includes one or more of Ni, Fe, Cr, Ti, Zn, V, Al, Mg, Zr and Ce, and B includes one or more of S, N, F, Cl, Br and I.

In some embodiments, the positive electrode material layer further includes a positive electrode binder and a positive electrode conductor, and the positive electrode active material, the compound shown in Structural Formula 1, the positive electrode binder and the positive electrode conductor are blended to obtain the positive electrode material layer.

Taking the total mass of the positive electrode material layer as 100%, the mass percentage of the positive electrode binder is 1-2%, and the mass percentage of the positive electrode conductor is 0.5-2%.

The positive electrode binder includes polyvinylidene fluoride, copolymers of vinylidene fluoride, polytetrafluoroethylene, copolymers of vinylidene fluoride-hexafluoropropylene, copolymers of tetrafluoroethylene-hexafluoropropylene, copolymers of tetrafluoroethylene-perfluoroalkyl vinyl ether, copolymers of ethylene-tetrafluoroethylene, copolymers of vinylidene fluoride-tetrafluoroethylene, copolymers of vinylidene fluoride-trifluoroethylene, copolymers of vinylidene fluoride-trichloroethylene, copolymers of vinylidene fluoride-fluoroethylene, copolymers of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene, thermoplastic polyimide, thermoplastic resins such as polyethylene and polypropylene; acrylic resin; sodium hydroxymethyl cellulose; polyvinyl butyral; ethylene-vinyl acetate copolymer; polyvinyl alcohol; and one or more of styrene butadiene rubber.

The positive electrode conductive agent includes one or more of conductive carbon black, conductive carbon balls, conductive graphite, conductive carbon fibers, carbon nanotubes, graphene or reduced graphene oxide.

In some embodiments, the compound represented by Structural Formula 1 is formed on the surface of the positive electrode material layer, or the compound represented by Structural Formula 1 is mixed in the interior of the positive electrode material layer.

When the compound represented by the structural formula 1 is formed on the surface of the positive electrode material layer, the preparation method thereof can refer to the following method:

A coating containing the compound shown in Structural Formula 1 is formed on the surface of the positive electrode material layer by surface coating. Specifically, the positive electrode active material, the positive electrode conductive agent and the positive electrode binder are first dispersed in an organic solvent to prepare a positive electrode slurry. After the positive electrode slurry is coated and dried to form a positive electrode material layer, the compound shown in Structural Formula 1 is dispersed in an organic solvent, and the obtained compound solution shown in Structural Formula 1 is sprayed on the surface of the positive electrode material layer. After drying and removing the solvent, the positive electrode material layer including the compound shown in Structural Formula 1 is obtained.

When the compound represented by the structural formula 1 is mixed in the interior of the positive electrode material layer, the preparation method thereof can refer to the following method:

1. The positive electrode slurry for preparing the positive electrode material layer contains the compound shown in structural formula 1. Specifically, the compound shown in structural formula 1, the positive electrode active material, the positive electrode conductive agent and the positive electrode binder are dispersed in an organic solvent to prepare the positive electrode slurry, and then the positive electrode slurry is coated and dried to form the positive electrode material layer;

2. After preparing the positive electrode material layer, immerse the positive electrode material layer in a solution containing the compound shown in Structural Formula 1 to allow the compound shown in Structural Formula 1 to penetrate into the interior of the positive electrode material layer, and dry and remove the solvent to obtain a positive electrode material layer containing the compound shown in Structural Formula 1.

In some embodiments, the positive electrode sheet further includes a positive electrode current collector, and the positive electrode material layer covers a surface of the positive electrode current collector.

The positive electrode current collector is selected from a metal material that can conduct electrons. Preferably, the positive electrode current collector includes one or more of Al, Ni, tin, copper, and stainless steel. In a more preferred embodiment, the positive electrode current collector is selected from aluminum foil.

The present invention also provides a secondary battery, comprising a negative electrode sheet, a non-aqueous electrolyte and a positive electrode sheet as described above, wherein the non-aqueous electrolyte comprises a non-aqueous organic solvent, and the non-aqueous organic solvent comprises a cyclic carbonate. The non-aqueous electrolyte contains a cyclic carbonate solvent with a relatively high dielectric constant, which can well form solvated lithium ion molecules with lithium ions. More preferably, the non-aqueous organic solvent also comprises a low-viscosity chain carbonate, which can improve the fluidity and wettability of the non-aqueous electrolyte.

In some preferred embodiments, the cyclic carbonate can be specifically but not limited to one or more of ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), and butylene carbonate (BC). The content of the cyclic carbonate is not particularly limited, and is arbitrary within the range that does not significantly damage the effect of the high-pressure lithium-ion battery of the present invention, but when one is used alone, the lower limit of its content is usually 3% or more by volume, preferably 5% or more by volume, relative to the total amount of solvent in the non-aqueous electrolyte. By setting this range, the decrease in conductivity caused by the decrease in the dielectric constant of the non-aqueous electrolyte can be avoided, and it is easy to make the large current discharge characteristics, stability relative to the negative electrode, and cycle characteristics of the non-aqueous electrolyte battery reach a good range. In addition, the upper limit is usually 90% or less by volume, preferably 85% or less by volume, and more preferably 80% or less by volume. By setting this range, the oxidation/reduction resistance of the non-aqueous electrolyte can be improved, thereby helping to improve the stability during high temperature storage.

In some preferred embodiments, the chain carbonate can be specifically but not limited to one or more of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and dipropyl carbonate (DPC). The content of the chain carbonate is not particularly limited, and relative to the total amount of solvent in the non-aqueous electrolyte, the volume ratio is usually more than 15%, preferably more than 20%, and more preferably more than 25%. In addition, the volume ratio is usually less than 90%, preferably less than 85%, and more preferably less than 80%. By making the content of the chain carbonate in the above range, it is easy to make the viscosity of the non-aqueous electrolyte reach an appropriate range, suppress the reduction of ionic conductivity, and then help to make the output characteristics of the non-aqueous electrolyte battery reach a good range. When two or more chain carbonates are used in combination, the total amount of the chain carbonate is allowed to meet the above range.

In certain embodiments, it is also possible to preferably use linear carbonates with fluorine atoms (hereinafter referred to as "fluorinated linear carbonates"). The number of fluorine atoms possessed by the fluorinated linear carbonates is not particularly limited as long as it is more than 1, but is generally less than 6, preferably less than 4. When the fluorinated linear carbonates have a plurality of fluorine atoms, these fluorine atoms can be bonded to the same carbon, or they can be bonded to different carbons. As the fluorinated linear carbonates, fluorinated dimethyl carbonate derivatives, fluorinated ethyl methyl carbonate derivatives, fluorinated diethyl carbonate derivatives, etc. can be enumerated.

In some embodiments, in addition to the cyclic carbonate solvent, the non-aqueous organic solvent further comprises one or more of an ether solvent, a nitrile solvent, and a carboxylate solvent.

In some embodiments, the ether solvent includes a cyclic ether or a chain ether, preferably a chain ether having 3 to 10 carbon atoms and a cyclic ether having 3 to 6 carbon atoms. The cyclic ether may be, but is not limited to, 1,3-dioxolane.

(DOL), 1,4-dioxane (DX), crown ether, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-CH ₃ -THF), 2-trifluoromethyltetrahydrofuran (2-CF ₃ -THF) or one or more thereof; the chain ether may specifically be, but is not limited to, dimethoxymethane, diethoxymethane, ethoxymethoxymethane, ethylene glycol di-n-propyl ether, ethylene glycol di-n-butyl ether, and diethylene glycol dimethyl ether. Since chain ethers have high solvation ability with lithium ions and can improve ion dissociation, dimethoxymethane, diethoxymethane, and ethoxymethoxymethane, which have low viscosity and can impart high ion conductivity, are particularly preferred. The ether compound may be used alone or in any combination and ratio. There is no special restriction on the amount of ether compounds added, and it is arbitrary within the range that does not significantly damage the effect of the high-density lithium-ion battery of the present invention. In the non-aqueous solvent volume ratio of 100%, the volume ratio is usually 1% or more, preferably 2% or more, and more preferably 3% or more. In addition, the volume ratio is usually 30% or less, preferably 25% or less, and more preferably 20% or less. When two or more ether compounds are used in combination, the total amount of the ether compounds can be made to meet the above range. When the amount of ether compounds added is within the above preferred range, it is easy to ensure the improvement of ion conductivity brought about by the increase in lithium ion dissociation degree and the decrease in viscosity of the chain ether. In addition, when the negative electrode active material is a carbon material, the phenomenon of co-embedding of chain ethers and lithium ions can be suppressed, so that the input-output characteristics and charge-discharge rate characteristics can reach an appropriate range.

In some embodiments, the nitrile solvent may specifically be, but is not limited to, one or more of acetonitrile, glutaronitrile, and malononitrile.

Carboxylate solvents include cyclic carboxylate and/or chain carbonate. Examples of cyclic carboxylate include one or more of γ-butyrolactone, γ-valerolactone, and δ-valerolactone. Examples of chain carbonate include one or more of methyl acetate (MA), ethyl acetate (EA), propyl acetate (EP), butyl acetate, propyl propionate (PP), and butyl propionate.

In some embodiments, the sulfone solvent includes a cyclic sulfone and a chain sulfone, but preferably, in the case of a cyclic sulfone, it is generally a compound having 3 to 6 carbon atoms, preferably 3 to 5 carbon atoms, and in the case of a chain sulfone, it is generally a compound having 2 to 6 carbon atoms, preferably 2 to 5 carbon atoms. There is no particular limitation on the amount of sulfone solvent added, and it is arbitrary within the range that does not significantly damage the effect of the high-pressure lithium-ion battery of the present invention. Relative to the total amount of solvent in the non-aqueous electrolyte, the volume ratio is generally 0.3% or more, preferably 0.5% or more, and more preferably 1% or more. In addition, the volume ratio is generally 40% or less, preferably 35% or less, and more preferably 30% or less. In the case of using two or more sulfone solvents in combination, the total amount of the sulfone solvents can be made to meet the above range. When the amount of sulfone solvent added is within the above range, an electrolyte with excellent high-temperature storage stability tends to be obtained.

In a preferred embodiment, the solvent is a mixture of cyclic carbonate and linear carbonate.

In some embodiments, the non-aqueous electrolyte further includes a lithium salt, and the lithium _salt includes one or more of _LiPF6 , _LiBOB , _LiDFOB , _LiPO2F2 , _LiBF4 , _LiSbF6 , _LiAsF6 , LiN( _SO2CF3 ) ₂ , LiN _{( SO2C2F5} ) ₂ , _{LiC (} SO2CF3) _{, LiN} (SO2F) _{2 , LiClO4} , _LiAlCl4 , _LiCF3SO3 , _Li2B10Cl10 , _and lower aliphatic carboxylic acid _lithium salts.

In a preferred embodiment, the non-aqueous electrolyte also includes a lithium salt, the lithium salt includes LiPF ₆ and an auxiliary lithium salt, the auxiliary lithium salt includes one or more of LiBOB, LiDFOB, LiPO ₂ F ₂ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiN(SO ₂ CF ₃ ) ₂ , LiN(SO ₂ C ₂ F ₅ ) ₂ , LiC(SO ₂ CF ₃ ) ₃ , LiN(SO ₂ F) ₂ , LiClO ₄ , LiAlCl ₄ , LiCF ₃ SO ₃ , Li ₂ B ₁₀ Cl ₁₀ , and lower aliphatic carboxylic acid lithium salts.

When the above conditions are met, adding _LiPF6 as the main lithium salt and the above auxiliary lithium salt to the non-aqueous electrolyte can further improve the thermal shock resistance of the battery. It is speculated that this is because the compound shown in structural formula 1 contained in the positive electrode is dissolved in a small amount in the non-aqueous electrolyte, and the combination with the above lithium salt has the effect of improving the stability of the non-aqueous electrolyte and avoiding the decomposition and gas production of the non-aqueous electrolyte.

In some embodiments, in the non-aqueous electrolyte, the added amount of LiPF ₆ is 0.1 mol/L to 3 mol/L, and the added amount of the auxiliary lithium salt is 0.05 mol/L to 1.5 mol/L.

In a preferred embodiment, in the non-aqueous electrolyte, the concentration of LiPF ₆ is 0.5 mol/L-2 mol/L. Specifically, the concentration of LiPF ₆ can be 0.5 mol/L, 1 mol/L, 1.5 mol/L, or 2 mol/L.

In a preferred embodiment, in the non-aqueous electrolyte, the concentration of the auxiliary lithium salt is 0.1 mol/L-1 mol/L. Specifically, the concentration of the auxiliary lithium salt may be 0.1 mol/L, 0.3 mol/L, 0.5 mol/L, or 1 mol/L.

In some embodiments, the non-aqueous electrolyte further comprises an auxiliary additive, wherein the auxiliary additive comprises at least one of a cyclic sulfate compound, a sultone compound, a cyclic carbonate compound, an unsaturated phosphate compound, and a nitrile compound;

Preferably, the cyclic sulfate ester compound is selected from at least one of vinyl sulfate, propylene sulfate or methyl vinyl sulfate;

The sultone compound is selected from at least one of 1,3-propane sultone, 1,4-butane sultone or 1,3-propylene sultone;

The cyclic carbonate compound is selected from at least one of vinylene carbonate, ethylene carbonate, fluoroethylene carbonate or the compound shown in structural formula 2.

In the structural formula 2, R ₂₁ , R ₂₂ , R ₂₃ , R ₂₄ , R ₂₅ , and R ₂₆ are each independently selected from a hydrogen atom, a halogen atom, and a C1-C5 group;

The unsaturated phosphate compound is selected from at least one of the compounds shown in Structural Formula 3:

In the structural formula 3, R ₃₁ , R ₃₂ , and R ₃₃ are each independently selected from a C1-C5 saturated hydrocarbon group, an unsaturated hydrocarbon group, a halogenated hydrocarbon group, and -Si(C _m H _2m+1 ) ₃ , m is a natural number of 1 to 3, and at least one of R ₃₁ , R ₃₂ , and R ₃₃ is an unsaturated hydrocarbon group;

In a preferred embodiment, the unsaturated phosphate compound may be at least one of tripropargyl phosphate, dipropargyl methyl phosphate, dipropargyl ethyl phosphate, dipropargyl propyl phosphate, dipropargyl trifluoromethyl phosphate, dipropargyl-2,2,2-trifluoroethyl phosphate, dipropargyl-3,3,3-trifluoropropyl phosphate, dipropargyl hexafluoroisopropyl phosphate, triallyl phosphate, diallyl methyl phosphate, diallyl ethyl phosphate, diallyl propyl phosphate, diallyl trifluoromethyl phosphate, diallyl-2,2,2-trifluoroethyl phosphate, diallyl-3,3,3-trifluoropropyl phosphate, and diallyl hexafluoroisopropyl phosphate.

The nitrile compound includes one or more of succinonitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrinitrile, adiponitrile, pimelonitrile, suberonitrile, azelaic acid dinitrile and sebaconitrile.

In other embodiments, the auxiliary additives may also include other additives that can improve battery performance: for example, additives that enhance battery safety performance, such as flame retardant additives such as fluorophosphates and cyclophosphazenes, or overcharge prevention additives such as tert-amylbenzene and tert-butylbenzene.

It should be noted that, unless otherwise specified, in general, the amount of any one of the optional substances in the auxiliary additives added to the non-aqueous electrolyte is less than 10%, preferably, the amount added is 0.1-5%, and more preferably, the amount added is 0.1% to 2%. Specifically, the amount of any one of the optional substances in the auxiliary additives can be 0.05%, 0.08%, 0.1%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 7.8%, 8%, 8.5%, 9%, 9.5%, 10%.

In some embodiments, when the auxiliary additive is selected from fluoroethylene carbonate, the amount of the fluoroethylene carbonate added is 0.05% to 30% based on the total mass of the non-aqueous electrolyte as 100%.

In some embodiments, the negative electrode sheet includes a negative electrode material layer, the negative electrode material layer includes a negative electrode active material, and the negative electrode active material is selected from at least one of a silicon-based negative electrode, a carbon-based negative electrode, a lithium-based negative electrode, and a tin-based negative electrode.

The silicon-based negative electrode includes one or more of silicon materials, silicon oxides, silicon-carbon composite materials and silicon alloy materials; the carbon-based negative electrode includes one or more of graphite, hard carbon, soft carbon, graphene and mesophase carbon microspheres; the lithium-based negative electrode includes one or more of metal lithium or lithium alloys. The lithium alloy can be at least one of lithium silicon alloy, lithium sodium alloy, lithium potassium alloy, lithium aluminum alloy, lithium tin alloy and lithium indium alloy. The tin-based negative electrode includes one or more of tin, tin carbon, tin oxide and tin metal compounds.

In some embodiments, the negative electrode material layer further includes a negative electrode binder and a negative electrode conductor, and the negative electrode active material, the negative electrode binder and the negative electrode conductor are blended to obtain the negative electrode material layer.

The selectable ranges of the negative electrode binder and the negative electrode conductor are the same as those of the positive electrode binder and the positive electrode conductor, respectively, and will not be described in detail herein.

In some embodiments, the negative electrode sheet further includes a negative electrode current collector, and the negative electrode material layer covers a surface of the negative electrode current collector.

The negative electrode current collector is selected from a metal material that can conduct electrons. Preferably, the negative electrode current collector includes one or more of Al, Ni, tin, copper, and stainless steel. In a more preferred embodiment, the negative electrode current collector is selected from copper foil.

In some embodiments, the battery further includes a separator, and the separator is located between the positive electrode sheet and the negative electrode sheet.

The diaphragm may be an existing conventional diaphragm, which may be a polymer diaphragm, a non-woven fabric, etc., including but not limited to single-layer PP (polypropylene), single-layer PE (polyethylene), double-layer PP/PE, double-layer PP/PP and triple-layer PP/PE/PP diaphragms.

The present invention is further described below by way of examples.

Table 1 Compounds of structural formula 1 used in the examples and comparative examples

Table 2 Design of Examples 1-25 and Comparative Examples 1-18

II. Preparation of Lithium Ion Batteries Used in Examples and Comparative Examples

1) Preparation of positive electrode

Step 1: Add PVDF as a binder and the unsaturated phosphate ester shown in Table 2 to NMP solvent, stir well to obtain PVDF glue solution added with unsaturated phosphate ester.

Step 2: Add the conductive agent (super P+CNT) into the PVDF glue and stir thoroughly.

Step 3: Continue to add the positive electrode active material shown in Table 2, stir thoroughly and evenly, and finally obtain the required positive electrode slurry. The added amounts of the compound shown in Structural Formula 1 and the positive electrode active material shall be based on the phosphorus and M element contents shown in Table 2.

Step 4: The prepared positive electrode slurry is evenly coated on the positive electrode current collector (such as aluminum foil), and the single-sided surface density of the coating is shown in Table 2. The positive electrode sheet is obtained by drying, rolling, die-cutting or striping.

2) Preparation of negative electrode

Step 1: Weigh each material according to the negative electrode sheet ratio of graphite (Shanghai Shanshan, FSN-1): conductive carbon (super P): sodium carboxymethyl cellulose (CMC): styrene-butadiene rubber (SBR) = 96.3:1.0:1.2:1.5 (mass ratio).

Step 2: First, add CMC into pure water at a solid content of 1.5%, and stir well (for example, stirring time 120 minutes) to prepare a transparent CMC glue solution.

Step 3: Add conductive carbon (super P) to the CMC glue solution and stir it thoroughly (for example, stirring time 90 minutes) to prepare a conductive glue.

Step 4: Continue to add graphite and stir thoroughly to finally obtain the required negative electrode slurry.

Step 5: Evenly coat the prepared negative electrode slurry on the copper foil, and obtain the negative electrode sheet by drying, rolling, die-cutting or striping.

3) Preparation of non-aqueous electrolyte

The solvents were mixed in the mass ratio shown in Table 2, additives were added in the mass percentages shown in Table 2, lithium hexafluorophosphate (LiPF ₆ ) was then added to a molar concentration of 1 mol/L, and auxiliary lithium salts and additives shown in Table 2 were added.

4) Lithium-ion battery cell preparation

The prepared positive electrode sheet and the negative electrode sheet are assembled into a laminated soft-pack battery cell.

5) Battery filling and formation

In a glove box with a dew point controlled below -40°C, the prepared electrolyte was injected into the battery cell, vacuum-sealed, and left to stand for 24 hours. Then, the conventional formation of the first charge was carried out according to the following steps: 0.05C constant current charging for 180 minutes, 0.2C constant current charging to 3.95V, secondary vacuum sealing, and then further 0.2C constant current charging to 4.2V, after standing at room temperature for 24 hours, 0.2C constant current discharge to 3.0V.

III. Performance Testing

The positive electrode sheets and batteries prepared in the above examples and comparative examples were subjected to the following performance tests:

1. High temperature cycle performance test of lithium-ion secondary batteries: At 45°C, charge the formed battery to 4.2V with 1C constant current and constant voltage, then charge it with constant voltage until the current drops to 0.05C, and then discharge it to 3.0V with 1C constant current. Repeat this cycle and record the first discharge capacity and the last discharge capacity.

The capacity retention rate of high temperature cycle is calculated as follows:

Capacity retention rate = last discharge capacity/first discharge capacity × 100%.

2. Thermal shock test of lithium-ion secondary battery: At 25°C, the lithium-ion secondary battery prepared in the embodiment and comparative example was placed for 5 minutes, charged to 4.2V at a constant current rate of 1C, and then charged to a current of less than or equal to 0.05C at a constant voltage, and then placed for 5 minutes. The lithium-ion secondary battery was then placed in an oven, and the oven temperature was set to rise from 25°C to 130°C at a heating rate of 2°C/min, and kept warm for 2 hours. The temperature of the battery surface and battery phenomena were monitored during the heating process and the insulation process.

(1) The performance test results of the lithium ion batteries prepared in Examples 1 to 7 and Comparative Examples 1 to 6 are shown in Table 3:

Table 3

It can be seen from Examples 1-7 and Comparative Examples 1-6 that when the type of positive electrode active material of the lithium ion secondary battery is the same, when the phosphorus content, manganese content and positive electrode single-sided surface density in the positive electrode material layer satisfy the preset relationship of 0.05≤p·u/v≤15, no runaway or fire occurs in the thermal shock test, and the lithium ion secondary battery has high safety performance, high temperature cycle performance and initial capacity performance.

It can be seen from the test results of Examples 1 to 7 that as the p·u/v value increases, the initial capacity, high-temperature cycle performance and heat shock resistance of the lithium-ion secondary battery first increase and then decrease, indicating that the phosphorus content, manganese content and single-surface surface density of the positive electrode in the positive electrode material layer are related to the electrochemical properties and safety performance of the lithium-ion secondary battery, especially when 0.5≤p·u/v≤5, the lithium-ion secondary battery has the best initial capacity, high-temperature cycle performance and heat shock resistance.

In the lithium-ion secondary batteries of comparative examples 1-3, the positive electrode material layer does not contain phosphorus, and the maximum surface temperature of the lithium-ion secondary batteries during thermal shock tests increases significantly, and smoke and fire occur, and the safety performance of the lithium-ion secondary batteries is low; in the lithium-ion secondary batteries of comparative example 4, since the phosphorus content in the positive electrode material layer is very low, the maximum surface temperature of the lithium-ion battery during thermal shock tests increases significantly, and smoke and fire occur, and the safety performance is low; in the lithium-ion secondary batteries of comparative examples 5-6, the phosphorus content in the positive electrode material layer is high, and the maximum surface temperature of the battery is low in the thermal shock test, and no runaway or fire occurs, but the phosphorus content, manganese content and single-sided surface density of the positive electrode in the positive electrode material layer do not satisfy the preset relationship of 0.05≤p·u/v≤15, the battery discharge capacity is low, and the cycle performance is not high, and the battery cannot take into account both electrochemical performance and safety performance.

From the test results of Comparative Example 2, Comparative Example 3 and Example 3, it can be seen that when the compound shown in Structural Formula 1 is added to the non-aqueous electrolyte, the performance improvement of the battery is far less than when the compound shown in Structural Formula 1 is added to the positive electrode material layer. This may be because the compound shown in Structural Formula 1 has a large viscosity and a low electrical conductivity. Adding it to the electrolyte will affect the battery's first efficiency, internal resistance, cycle and other performance.

(2) The performance test results of the lithium ion batteries prepared in Examples 2-4 and Comparative Examples 7-9 are shown in Table 4:

Table 4

From the test results of Examples 2-4 and Comparative Examples 7 to 9, it can be seen that when no cyclic carbonate solvent is used in the electrolyte, the capacity retention rate is significantly reduced after high-temperature cycling. It is speculated that this may be because the absence of cyclic carbonates will lead to low electrolyte conductivity, fewer mobile lithium ions, and an inability to form a stable SEI film. The battery polarization phenomenon is serious and will lead to lithium deposition in the battery, causing premature decay of the battery cycle.

(3) The performance test results of the lithium ion batteries prepared in Examples 3, 8 to 11 and Comparative Examples 1, 10 to 13 are shown in Table 5:

Table 5

It can be seen from the test results of Examples 3 and 8 to 11 that in a battery containing the positive electrode provided by the present invention, adding the above-mentioned additives DTD (vinyl sulfate), VC (vinyl carbonate), FEC (fluoroethylene carbonate) or PS (1,3-propane sultone) to the non-aqueous electrolyte can further improve the high-temperature cycle performance of the battery and reduce the maximum surface temperature of the battery in the thermal shock test. It is speculated that the compound shown in structural formula 1 in the positive electrode and the above-mentioned additives jointly participate in the formation of the passivation film on the electrode surface, thereby obtaining a passivation film with excellent thermal stability, thereby effectively reducing the reaction of the electrolyte on the electrode surface and improving the safety of the battery.

More preferably, among the above additives, it can be seen that the use of DTD in combination with a positive electrode containing the compound represented by structural formula 1 has the most significant effect on improving the high temperature cycle performance and heat shock resistance of the battery.

(4) The performance test results of the lithium ion batteries prepared in Examples 3, 12 to 14 are shown in Table 6:

Table 6

It can be seen from the test results of Examples 3 and 12-14 that in the battery containing the positive electrode provided by the present invention, adding the above-mentioned auxiliary lithium salt LiDFOB, LiBOB or _LiPO2F2 to the non-aqueous electrolyte can further improve the high-temperature cycle performance of the battery and reduce the maximum surface temperature of the battery in the thermal shock test. It is speculated that this is because the compound represented by structural formula ₁ in the positive electrode is partially dissolved in the non-aqueous electrolyte and forms a good coordination relationship with the lithium salt of a specific combination, which is beneficial to improving the stability of the non-aqueous electrolyte.

More preferably, among the auxiliary lithium salts mentioned above, it can be seen that the combination of LiPF ₆ and LiPO ₂ F ₂ has the most obvious effect on improving the heat resistance of the battery.

(5) The performance test results of the lithium ion batteries prepared in Examples 3, 15 to 18 are shown in Table 7:

Table 7

It can be seen from the test results in Table 7 that for different compounds represented by structural formula 1, when the phosphorus content, manganese content and single-surface surface density of the positive electrode in the positive electrode material layer satisfy the preset relationship of 0.05≤p·u/v≤15, the effects they play are similar, and both have a certain improvement effect on the battery capacity and safety of the battery, indicating that the relationship provided by the present invention is applicable to different compounds represented by structural formula 1.

(6) The performance test results of the lithium ion batteries prepared in Examples 19 to 28 and Comparative Examples 14 to 21 are shown in Table 8:

Table 8

It can be seen from the test results of Example 19 and Comparative Example 14 that the M element in the positive electrode active material is Al. When the phosphorus content, aluminum content and single-sided surface density of the positive electrode in the positive electrode material layer satisfy the preset relationship of 0.05≤p·u/v≤15, the battery also has good high-temperature cycle performance and thermal shock resistance.

It can be seen from the test results of Examples 20-23 and Comparative Examples 15 and 16 that when LiNi _0.5 Co _0.2 Mn _0.3 O ₂ is used as the positive electrode active material, when the phosphorus content, aluminum content and positive electrode single-surface density in the positive electrode material layer satisfy the preset relationship 0.05≤p·u/v≤15, the battery also has good high-temperature cycle performance and thermal shock resistance.

It can be seen from the test results of Examples 24-28 and Comparative Examples 17-21 that when the manganese content of the positive electrode sheet in the lithium ion secondary battery is high, even if the compound shown in Structural Formula 1 is not added to the positive electrode sheet, no smoking or fire will occur, indicating that a high content of manganese can improve the structural stability of the positive electrode active material and reduce the decomposition and deoxygenation of the positive electrode active material, but the energy density of the battery is reduced. When the compound shown in Structural Formula 1 is added to the positive electrode sheet, a stable solid electrolyte interface film containing phosphorus can be formed in the positive electrode material layer, and the interface film can inhibit excessive side reactions between the positive electrode active material and the electrolyte. Further, through the design of the single-sided surface density of the positive electrode, the three synergistically inhibit the gas production of the battery and reduce the heat generation, thereby reducing the risk of runaway of the lithium ion secondary battery, improving the high-temperature cycle performance of the lithium ion secondary battery, and also making the lithium ion secondary battery have higher safety performance and energy density.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims (10)

1. A secondary battery positive electrode sheet, including a positive electrode material layer, characterized in that the positive electrode material layer includes a positive electrode active material and a compound represented by structural formula 1: Among them, R ₁ , R ₂ and R ₃ are each independently selected from an alkyl group of 1-5 carbon atoms, a fluoroalkyl group of 1-5 carbon atoms, an ether group of 1-5 carbon atoms, A fluorinated ether group of 2 to 5 carbon atoms, an unsaturated hydrocarbon group of 2 to 5 carbon atoms, and at least one of R ₁ , R ₂ , and R ₃ is an unsaturated hydrocarbon group of 2 to 5 carbon atoms; A coating containing the compound represented by Structural Formula 1 is formed on the surface of the cathode material layer by surface coating, or the compound represented by Structural Formula 1 is mixed inside the cathode material layer; The positive active material includes M element, and the M element is selected from one or two types of Mn and Al; The positive active material includes one or more compounds represented by formula (1) and formula (2); Li _1+x Ni _a Co _b M _1-ab O _2-y A _yFormula (1) Li _1+z Mn _c L _2-c O _4-d B _dFormula (2) In formula (1), -0.1≤x≤0.2, 0<a<1, 0≤b<1, 0<a+b<1, 0≤y<0.2, M includes one or more of Mn and Al species, and optionally include zero, one or more of Sr, Mg, Ti, Ca, Zr, Zn, Si, Fe, Ce, A includes S, N, F, Cl, Br and I one or more; In formula (2), -0.1≤z≤0.2, 0<c≤2, 0≤d<1, L includes one of Ni, Fe, Cr, Ti, Zn, V, Al, Mg, Zr and Ce or more, B includes one or more of S, N, F, Cl, Br and I; The positive electrode material layer meets the following conditions: 0.05≤p·u/v≤15 Among them, u is the mass percentage of phosphorus element in the cathode material layer, the unit is wt%; v is the mass percentage of M element in the cathode material layer, the unit is wt%; p is the single surface density of the positive electrode material layer, in mg/cm ² ; In the above relational formula, the phosphorus element in the cathode material layer only represents the phosphorus element derived from the compound shown in Structural Formula 1, and the M element in the cathode material layer only represents the Mn and/or Al element derived from the cathode active material; In the positive electrode material layer, the mass percentage u of phosphorus element is 0.1wt%~3wt%; In the positive electrode material layer, the mass percentage v of the M element is 3wt% to 60wt%; The single surface density p of the positive electrode material layer is 10 to 30 mg/cm ² . 2. The secondary battery cathode sheet according to claim 1, wherein the cathode material layer satisfies the following conditions: 0.1≤p·u/v≤10. 3. The secondary battery cathode sheet according to claim 1, wherein the cathode material layer satisfies the following conditions: 0.5≤p·u/v≤5. 4. The secondary battery positive electrode sheet according to claim 1, wherein the compound represented by the structural formula 1 includes trialpargyl phosphate, dipropargyl methyl phosphate, and dipropargyl methyl fluoride. phosphate, dipropargyl methoxymethyl phosphate, dipropargyl ethyl phosphate, dipropargyl propyl phosphate, trifluoromethyl dipropargyl phosphate, dipropargyl 2 ,2,2-trifluoroethyl phosphate, dipropargyl 3,3,3-trifluoropropyl phosphate, hexafluoroisopropyl dipropargyl phosphate, triallyl phosphate, diallyl Diallyl methyl phosphate, diallyl ethyl phosphate, diallyl propyl phosphate, trifluoromethyl diallyl phosphate, 2,2,2-trifluoroethyl diallyl phosphate Ester, diallyl methyl ether phosphate, dipropargyl fluoromethyl ether phosphate, diallyl 3,3,3-trifluoropropyl phosphate or diallyl hexafluoroisopropyl phosphate at least one of them. 5. The secondary battery cathode sheet according to claim 1, wherein the surface of the cathode material layer is detected by X-ray photoelectron spectroscopy. When the 1s peak of carbon is obtained at 284.5eV, it is between 130 and 130 eV. The characteristic peak of phosphorus element appears in the 140eV region. 6. The secondary battery cathode sheet according to claim 1, wherein the mass percentage u of phosphorus element in the cathode material layer is 0.1 wt% to 2 wt%. 7. The secondary battery cathode sheet according to claim 1, wherein the mass percentage v of the M element in the cathode material layer is 3wt% to 30wt%. 8. The secondary battery cathode sheet according to claim 1, wherein the single surface density p of the cathode material layer is 15-20 mg/cm ² . 9. A secondary battery, characterized by comprising a non-aqueous electrolyte and the secondary battery positive electrode sheet according to any one of claims 1 to 8, the non-aqueous electrolyte comprising a non-aqueous organic solvent, Non-aqueous organic solvents include cyclic carbonates. 10. The secondary battery according to claim 9, wherein the non-aqueous electrolyte further includes a lithium salt, and the lithium salt includes LiPF ₆ , LiBOB, LiDFOB, LiPO ₂ F ₂ , LiBF ₄ , LiSbF _6. LiAsF ₆ , LiN(SO ₂ CF ₃ ) ₂ , LiN(SO ₂ C ₂ F ₅ ) ₂ , LiC(SO ₂ CF ₃ ) ₃ , LiN(SO ₂ F) ₂ , LiClO ₄ , LiAlCl ₄ , LiCF ₃ One or more of SO ₃ , Li ₂ B ₁₀ Cl ₁₀ , and lower aliphatic carboxylic acid lithium salt.